In microwave technology, it has become technically feasible to integrate circuits in commercial packages for volume manufacturing and sale. Previously it was necessary to design a layout and mount discrete components on that layout, where a matching procedure often was necessary afterwards in order to tune the circuit. These packaged integrated microwave circuits thus make microwave design easier and cheaper than before.
A number of such packages have been developed during the last years. A package normally comprises a circuit with etched components on a silicon substrate, constituting a microwave chip. A package normally further comprises a carrier, for example in the form of a microwave laminate, to which the chip is fixed. The chip comprises connecting points, which are connected to connecting points on the laminate by means of bonding, using very thin gold wires. The laminate communicates its connecting points via a plurality of connectors, accessible for a user. The laminate and its chip are normally provided with a protective covering, for example an epoxy resin, a plastic cover shell, or both.
One such type of package is the so-called BGA (Ball Grid Array) package, which is an encapsulated circuit with a more or less complete M×N array of connectors on its lower side, constituting a so-called footprint. The connectors are in the form of balls which stands out a certain distance from the package. A circuit board on which the package is to be mounted has a corresponding soldering pattern comprising corresponding soldering pads, matching the footprint—one pad for each ball-shaped connector on the package. An adhesive soldering paste is dispensed on each pad. The package is placed on the circuit board in such a way that the ball-shaped connectors contact the desired corresponding soldering pads. Then the circuit board is gently heated in such a way that the balls and the soldering paste melts, followed by cooling, where the pads and the connectors now are soldered together.
The solder joint more or less preserves its spherical shape, creating a stand-off between the package and the circuit board. This is, however, disadvantageous at higher frequencies, since this stand-off constitutes an inductance which is difficult to predict with sufficient accuracy.
Another type of package is called QFN (Quad Flat No lead) which is rectangular with connectors arranged at all four sides. The connectors do not extend out from the outline of the package, but extend at least partly along the lower side of the package. The chip is glued to a laminate, and its connecting points are connected to connecting points on the laminate by means of bonding, using very thin gold wires. The connecting points on the laminate are in turn connected to the connectors of the package by means of via holes that extend from the top of the laminate where its bond-connected connecting point is positioned, to the lower side of the laminate, where the connector is positioned.
This configuration is, however, disadvantageous since there are two inductances present for each connection; the bond wire and the via. The higher frequency, the more problematic do these inductances become for designing an accurate, repeatable construction.
One other type of package is called flip-chip, and comprises a chip of BGA type, but much more miniaturized. The chip is soldered as an ordinary BGA package to a laminate in order to constitute either a BGA package or a QFN package.
If it is a BGA package, there are problems with stand-off distances for the ball connectors at the chip as well as at the lower side of the laminate. There are also vias connecting between connecting points on the upper side of the laminate, and the ball connectors on the lower side of the laminate.
If it is a QFN package, there are problems with stand-off distances for the ball connectors at the chip and those vias connecting between connecting points on the upper side of the laminate, and the connectors on the lower side of the laminate.
As described in U.S. Pat. No. 6,011,692, which is considered as closest prior art, a chip is bonded to connectors at a supporting element into which the chip is fastened. The bottom of the chip rests on a conductive foil. The supporting element is lowered into a recess in a circuit board with a ground plane. In the recess, the dielectrica of the circuit board is completely removed, allowing the lowered supporting element to rest on the conducting foil constituting the ground plane of the circuit board. In this way, the ground of the chip is easily connected to the circuit board ground. The connectors of the supporting element are connected to conductors at the circuit board via conductors, soldered or glued in place.
Although the known device functions in a satisfactory manner, there are certain aspects which can be improved, for example:                A glue or solder has to be applied to the conductors on the supporting structure, and may interfere with the chip and/or bond wires.        The transmission lines are broken by solder or glue joints at two places after the bond wires        When mounting the supporting structure with its chip, the circuit board has to be brought through two runs in a pick-n-place machine and solder dispenser.        The bond wires are unprotected if no lid is positioned over the supporting structure        Should a lid be placed over the supporting structure, the lid will be in contact with the conductors        